This invention relates to microfiche readers and more particularly to the focusing system used in such readers for projecting images photocopied on microfiche.
Microfiche film is a known form of graphic data presentation wherein a number of pages or images are photographically reproduced on a single "card" of microfiche film (such as a card of 3 inches .times. 5 inches to 4 inches .times. 6 inches, for example). Any suitable number of pages (up to, say, a thousand or so) may be photographically formed in an orthogonal array on a single microfiche card of photographic film. The microfiche film may then be placed in an optical reader and moved over a rectilinear path until an image or a selected page is in an optical projection path leading to a display screen.
It is uneconomical to provide a microfiche reader system for a single microfiche card; therefore, the user is likely to have an entire library file made up of many microfiche cards which must be kept in a specific order for quick recall. Therefore, microfiche readers are adapted to file and store a quantity of microfiche in a library file, remove and mechanically manipulate the microfiche, and then refile it in the library file. The mechanical manipulation of a microfiche involves sliding the microfiche into and out of the library file, moving it in a path in X and Y directions, and projecting a selected image in the orthogonal array through the optical path of a projector. Hence, mechanical microfiche reader equipment may be designed to find and select the desired one of the many microfiche images in the library file and to project it without damage. Then, the microfiche must be safely returned to the library file for storage.
The preferred reader is a compact unit which may be carried about if need be. The optical path must be long enough to increase the very small photocopy image to an easily readable compact unit.